1. Field of the Invention
The present invention relates to an imaging system and more specifically to a method and device for developing and transferring an image in an image recording device.
2. Discussion of Related Art
A device is known as described in Japanese Publication 55/43536, in which the circumferential speed of a photoconductive drum is detected and in which the supply of data to a laser scan module is controlled in connection with the drum speed. The speed of the receiving sheet to which a toner image is transferred is also controlled on the basis of the detected circumferential speed of the drum near the image transfer station. Although in this way a correction is made for the photoconductive drum being out of round, various kinds of unwanted effects occur, nevertheless, particularly at the transfer station to prevent accurately synchronized image transfer. For example, the receiving sheet, which is fed on a belt, will generally always experience some slippage in the transfer zone, thus resulting in image distortion. In addition, if the image is transferred to a thick receiving sheet, the surface speed of that sheet in the transfer zone will be greater than that of a thin receiving sheet. Particularly in the case of printing devices used in drawing offices, it is a requirement that a print on a receiving sheet differ very little from the original. The length of the image on the copy may deviate only by 0.3% at a maximum. This requirement applies to all kinds of receiving sheets processed in the printing device, in formats A0 to A4, thicknesses of from 0.06 to 0.25 mm, transparent films, and so forth. In order to satisfy this very high requirement for a 1:1 image, some known printing devices comprise a control element which can be adjusted by the operator by means of which, for example, the speed of the receiving material can be adjusted by means of a fine control. To this end, the operator measures the dimensions of the resulting image on the printed medium and compares them with the dimensions of the original. This operation must be repeated for the subsequent prints until an exact 1:1 image is obtained.
Satisfying this high imaging accuracy becomes even more difficult if use is made of transfer devices of the kind described, for example, in U.S. Pat. No. 4,541,709. Therein, the powder image on a photoconductive belt is first transferred to an intermediate member such as a belt having a top layer of silicone rubber. This belt is heated and the toner image thus softened is transferred to a receiving sheet. Accordingly, the top layer is pressed in somewhat as a result of the pressure at the contact surface of the intermediate member and the photoconductive belt, so that the toner image transferred to the intermediate member is some percent longer than the original image. An opposite effect occurs on transfer to the receiving sheet, but complete compensation does not occur owing to the differences in pressure between the two contact surfaces. The image deformation (image lengthening or shortening) is, to a high degree, pressure-dependent. For example, on transfer to a thick receiving sheet the deformation will be different from that occurring in the case of transfer to a thin receiving sheet. The same kind of variation occurs on transfer to a large format (A0) or a small format (A4) receiving sheet.
Another disadvantage of the known systems is that the transfer rollers and the like exhibit some degree of wear during their life and thus decrease in thickness. This, in turn, has the effect that for an originally, correctly adjusted speed of rotation, the circumferential speed of the rollers decreases, so that, for example, the receiving sheets are supplied at a reduced speed, so that there is again a deformation of the transferred image.